There is a technique to detect phase currents that flow through a three-phase load by using a shunt resistance. In a configuration provided with a shunt resistance, a power-supply shunt resistance that detects an electric current flowing between a direct-current power supply and an inverter device is provided (hereinafter, this configuration is referred to as “single-shunt current detection method”). In this case, the phase of a load current that flows through the power-supply shunt resistance is changed in accordance with the state of an inverter output voltage, that is, the on-state or off-state of inverter switching elements. Thus, a voltage drop at the power-supply shunt resistance is detected in accordance with the on-state or off-state of the inverter switching elements, and thereby the load current can be detected.
Meanwhile, the single-shunt current detection method has a problem in that it may be difficult to detect electric currents for two phases depending on the phase of the inverter output voltage. As a solution to this problem, the following two Patent Literatures are disclosed, for example.
Non Patent Literature 1 listed below is a publicly-known document related to an interior permanent magnet synchronous motor. Non Patent Literature 1 is mentioned later in “Description of Embodiments”.